Some blood pumps mimic the pulsatile flow of the heart and have progressed to designs that are non-pulsatile. Non-pulsatile or continuous flow pumps are typically rotary and propel fluid with impellers that span the spectrum from radial flow centrifugal type impellers to axial flow auger type impellers.
A common issue encountered by blood pumps is blood damage. The causes of blood damage are mostly attributed to shear stress and heat generated by the bearings supporting the impeller and/or shaft seals of externally driven impellers. Shear stress and/or heat may cause hemolysis, thrombosis, and the like.
A great deal of effort has been devoted to reducing or eliminating blood damage in rotary blood pumps. One solution to minimizing/eliminating blood damage is to provide total hydrodynamic support of the impeller. For example, ramp, wedge, plain journal, or groove hydrodynamic bearings may be utilized to provide hydrodynamic support in blood pumps.
Additionally, passive permanent magnetic and active controlled magnetic bearings can be utilized to provide impeller support in blood pumps. Magnetic bearings may be combined with hydrodynamic bearings to provide total impeller support in blood pumps.
Some blood pumps provide blood flow utilizing a motor that has a shaft mechanically connected to an impeller. Shaft seals may be utilized to separate the motor chamber from the pump chamber. However, shaft seals can fail and generate excess heat allowing blood to enter the motor and/or produce blood clots. Some blood pumps incorporate electric motors into the pumping chamber, rather than providing separate motor and pumping chambers. For example, a stator may be provided in the pump housing and magnets can be incorporated into an impeller to provide a pump impeller that also functions as the rotor of the electric motor.
Heart pumps that are suitable for adults may call for approximately 5 liters/min of blood flow at 100 mm of Hg pressure, which equates to about 1 watt of hydraulic power. Some implantable continuous flow blood pumps consume significantly more electric power to produce the desired amount of flow and pressure.
High power consumption makes it impractical to implant a power source in the body. For example, size restrictions of implantable power sources may only allow the implantable power source to provide a few hours of operation. Instead, high power consumption blood pumps may provide a wire connected to the pump that exits the body (i.e. percutaneous) for connection to a power supply that is significantly larger than an implantable power source. These blood pumps may require external power to be provided at all times to operate. In order to provide some mobility, external bulky batteries may be utilized. However, percutaneous wires and external batteries can still restrict the mobility of a person with such a blood pump implant. For example, such high power consumption blood pumps have batteries that frequently require recharging thereby limiting the amount of time the person can be away from a charger or power source, batteries that can be heavy or burdensome thereby restricting mobility, percutaneous wires that are not suitable for prolonged exposure to water submersion (i.e. swimming, bathing, etc.), and/or other additional drawbacks.
The various embodiments of blood pumps discussed herein may be suitable for use as a ventricular assist device (VAD) or the like because they cause minimal blood damage, are energy efficient, and can be powered by implanted batteries for extended periods of time. Further, these pumps are also beneficial because they may improve the quality of life of a patient with a VAD by reducing restrictions on the patient's lifestyle.